The issuers are only "required" to issue tax forms for amounts greater than $10.
But
Even if you don't get a form, you are supposed to report any amounts distributed that are 50 cents or greater.
A common example would checking account interest, which have pitifully low interest earning rates. You may only get a dollar or two in interest during the year...it is most likely that no 1099-INT will be issued for that, but you are still supposed to report that interest (if 50 cents or higher) as a 1099-INT, from that bank, on your tax return.